The present invention relates generally to an automotive suspension system for suspending road wheels from a vehicle body, which suspension system includes a vehicle height control mechanism and a damping force adjusting mechanism. More particularly, the invention relates to a suspension system for an automotive vehicle with a vehicle height control mechanism associated with a damping force adjusting mechanism for varying the damping force produced by vehicle dampers in correspondence with the height of the vehicle body with respect to the road surface.
Vehicle height adjusting mechanisms or vehicle level regulators are known in various guises. For example, U.S. Pat. No. 4,327,936, issued on May 4, 1982 to Sekiguchi, discloses a height control system for an automotive vehicle with an air dehumidifying arrangement. The disclosed system includes a vehicle height detector for detecting variations in the height of the vehicle body and a pneumatically controlled damper for raising and lowering the vehicle in correspondance with the detected vehicle level. For instance, when the detector detects that the vehicle is lower than a predetermined lower limit, the detector produces a signal demanding increase in the pressure in the damper to raise the vehicle body, and when the detector detects that the vehicle is higher than a predetermined upper limit, then the detector produces a down command to reduce the pressure in the damper and thus lower the vehicle. Thus the disclosed height control system can maintain the vehicle height or level to within a predetermined height range defined by the aforementioned lower and upper limits.
In general, such height control systems are used to regulate the vehicle level when significantly heavy loads are applied to the vehicle, which might otherwise excessively lower the vehicle. However, in recent years, height control systems have also been used to improve aerodynamics and driving stability. For the latter purpose, the recently developed height control systems are equipped with a vehicle speed-dependent height-adjusting mechanism. This vehicle speed-dependent height adjustment means that the vehicle is lowered by a predetermined amount when the vehicle is travelling at a speed above a given speed, e.g., 80 km/h.
Dampers applicable for vehicle height control have pneumatic chambers the pressure within which can be adjusted in the manner set forth above in order to adjust the vehicle height. As the pressure in the pneumatic chamber increases, the damper becomes more rigid. This may cause a rough-ride feeling for the vehicle occupants. On the other hand, as the pressure in the pneumatic chamber decreases, the damping force generated by the damper also decreases, thus degrading driving stability. In particular, if the vehicle level is reduced while the vehicle is moving at a speed higher than the above given speed, driving stability would be significantly degraded due to insufficient damping force and increased tendency toward roll steering. In order to achieve driving stability and a greater cornering force restricting roll steering, the damper or suspension coils may be selected to produce a greater damping force. However, in this case, when the vehicle height is adjusted upwards, the damping force may be so great as to provide a rough ride.